Stop wearing elevation masks

They don’t mimic high altitudes.

The reason it’s more challenging to breathe in the mountains is because there’s less oxygen in the air. When you live at high altitudes, your body compensates for that by producing more erythropoietin (EPO) to increase the amount of oxygen in your blood.

Then, when mountain-dwellers head back down to sea level, the higher oxygen-to-blood ratio ups their VO2 max, which makes intense workouts (including races) feel easier. Some people try to get the same benefits by wearing elevation masks at sea level.
Wearing an elevation mask doesn’t mimic living at altitude. “The effect it has is air restriction,” says David Otey, CSCS, personal training manager at Equinox Sports Club Upper West Side in New York City. That makes your workout more challenging in the moment, but it doesn’t translate to the long-term benefits.

A 2016 study found that training in elevation masks for six weeks had no effect on VO2 max, and 2017 research showed that people’s VO2 max improved after six weeks of HIIT regardless of whether they wore a mask or not.
To get the VO2 max benefits of high-altitude training, you have to actually live in high altitudes. “The only real advantage of training with an elevation mask on is learning to push through barriers with restricted breath,” Otey says.